There are specific cautions on doing this test at speeds above idle in the
Detroit shop manual that I have, and the reason is the blower oil seals.
The engine will draw vacuum against the shaft seals in the blower and they
are not designed to seal against that.

2-stroke diesels do not produce a vacuum.

NetSock wrote:
2-stroke diesels do not produce a vacuum.

The Roots type blower used to provide scavenging air to many 2-stroke
diesels will produce a very high vacuum.

I can attest to the fact that a runaway 2-stroke will pull enough vacuum
to crush and collapse many feet of sheet metal intake trunking.

Rick

"Rick" wrote in message
ink.net...
NetSock wrote:
2-stroke diesels do not produce a vacuum.

The Roots type blower used to provide scavenging air to many 2-stroke
diesels will produce a very high vacuum.

I can attest to the fact that a runaway 2-stroke will pull enough vacuum
to crush and collapse many feet of sheet metal intake trunking.

Rick

Oh! In that sense you are correct. I was referring to the internal (past the
blower) 2-stroke diesel engine. There is never a vacuum against the intake
ports, or in the cylinders. In fact, the plenum is always "pressurized" when
running.

Past the blower, a 2-stoke diesels do not produce a vacuum.

NetSock wrote:

Past the blower, a 2-stoke diesels do not produce a vacuum.

No one ever said they did. Karl was talking about the blower and what
occurred within the blower housing.

But since you brought it up ... 8-)

Quite a few early 2-stroke diesel engines produced a vacuum without
benefit of roots or any blowers at all.

Rick

"NetSock" wrote in message ...
There are specific cautions on doing this test at speeds above idle in the
Detroit shop manual that I have, and the reason is the blower oil seals.
The engine will draw vacuum against the shaft seals in the blower and they
are not designed to seal against that.

2-stroke diesels do not produce a vacuum.

There is a vacuum produced "upstream" of the blower - the fact that
the blower is sucking air into the engine tells you there is a vacuum
somewhere. It just isn't produced by descending pistons.